A cigarette typically includes a tobacco rod and a filter connected to the tobacco rod. A smoker ignites one end of the tobacco rod and draws smoke in through the filter.
In a known arrangement, for example UK patent application GB-A-2133269, the filter includes a porous inner material sheet (sometimes referred to as a plug wrap) which wraps the filter rod. The porous inner material sheet is situated between the filter rod and an outer wrapper (sometimes referred to as tipping paper). The inner material sheet is shaped to form a number of grooves which extend from the mouth end of the filter along the axis of the filter and terminate before the tobacco rod end of the filter. When the cigarette is smoked, smoke is drawn from inside the filter rod through the inner material sheet and along the grooves. There is an increased deposition of smoke constituents where the smoke passes through the inner material sheet, due both to the resistance of the sheet material itself, and also to the sudden acceleration of smoke as it enters the grooves.
In many cigarettes, the outer wrapper is wrapped completely around the cigarette and then is glued to itself by a line of adhesion running along the length of the filter. The adhesion process may involve applying pressure along the line of adhesion, which may cause some of the grooves in the inner material sheet underneath the line of adhesion to get crushed and therefore blocked. This may impact the filtration behaviour of the filter and the visual quality of the filter.